1. Field of the Invention
The present invention relates to a method and apparatus for the suspension smelting of sulfidic raw materials containing metals, such as copper, nickel and lead, when a high degree of oxygen enrichment is employed in the oxidizing gases to be fed in the smelting unit in order to raise the temperature of the particles in suspension.
2. Description of the Related Art
In traditional suspension smelting, the finely divided sulfidic raw material containing metals such as copper, nickel and lead, the recirculated flue dust and fluxes, as well as the air and/or oxygen mixture to be used as the oxidizing gas, either preheated or cold, are conducted to the vertical reaction shaft of a suspension smelting furnace from top to bottom, so that the oxidizing reactions take place at a high temperature. Owing to the influence of reaction heat and possible additional fuel, the major part of the reaction products will melt. From the reaction shaft the suspension falls into the horizontal part of the furnace, i.e. to the settler, which contains at least two but sometimes three molten layers. If the settler contains three molten layers, the lowermost layer is the raw metal layer. Most often there are only two layers in the furnace: lowermost the matte or metal layer, and the slag layer on top of it. The majority of the molten or solid particles in suspension falls directly to the melt located underneath the reaction shaft at roughly the slag temperature, and the most finely divided ingredients continue along with the gases towards the other end of the furnace. All along the way, the suspension particles are settled into the melt of the settler. From the other end of the settler, the exhaust gases are conducted directly up through the uptake shaft of the suspension smelting furnace, wherefrom the gases are further conducted to a gas processing arrangement comprising a waste heat boiler and an electrofilter. Generally the smelting in the suspension smelting furnace is attempted to be carried out as autogeneously as possible, without external fuel, by preheating and/or oxygen enriching the oxidizing gas to be fed into the reaction space.
The reactions that are started in the reaction space, i.e. reaction shaft of the suspension smelting furnace, are completed after the particles have fallen into the melt contained in the settler of the suspension smelting furnace. In order to compensate heat losses and to provide for the settler reactions, oil is fed into the settler through burners connected to the walls, both to underneath the reaction shaft and to other parts of the settler. The burning of oil does, however, increase the water content in the gas discharged from the suspension smelting furnace, which is harmful with respect to further treatment of the gas. At the same time the total amount of gas discharged from the suspension smelting furnace increases, because air is used in the combustion. The high total gas amount also reduces the smelting capacity in suspension smelting, which further increases the operation costs of suspension smelting, as well as the total costs thereof.
In addition to the most finely divided particle fraction of suspension, also those particles that did not react and melt in the reaction shaft tend to follow the gas flow out of the suspension smelting furnace, because their area/weight ratio is higher than that of the molten particles. The particles are separated from the gas phase in the exhaust gas processing arrangement, in the waste heat boiler and electrofilter, together with the most finely divided particle fraction of the suspension. In the gas processing arrangement, the separated solids, i.e. flue dust, are returned to the suspension smelting furnace. The recirculation of flue dust increases the energy demand in the reaction shaft of the suspension smelting furnace, which demand is normally covered by feeding additional fuel. An increased use of additional fuel increases the total gas amount in the suspension smelting furnace and reduces the molten amount of the original sulfidic raw material.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved method and apparatus for the suspension smelting of sulfidic raw materials containing metals, such as copper, nickel and lead, so that the reactions taking place in the reaction shaft of the suspension smelting furnace, as well as the melting of the particles, can advantageously be completed before the particles fall into the settler of the suspension smelting furnace.